The increase in the operating frequency and projected die size of CMOS circuits to 10 cm2 or more has led to the proposal of wireless interconnects based on integrated antennas. Integrated antennas can provide a high speed alternative to a conventional wired interconnection system through use of free-space (e.g. microwave) communications which travel at nearly the speed of light. Wireless communications can be both within an IC and between ICs.
The antenna gain is one of the key factors determining the feasibility of an integrated system based on integrated antennas. Such integrated systems can include one or more electronic devices, such as microprocessors. If the antenna gain can be increased, the distance between communication points within the overall circuit or circuits can be increased, or the signal quality (e.g. signal to noise ratio) can be enhanced for a constant spacing distance between communicating elements.
Previous work has inserted dielectric layers, such as wood or glass blocks, between the wafer containing the integrated antenna and a metallic heat sink to increase the antenna gain. Antenna gain is increased in this case because a low loss dielectric propagation layer is provided for the electromagnetic fields as they are guided by the antenna elements.
A low loss dielectric propagating layer can reduce the influence of the lossy metal heat sink layer generally disposed below the integrated circuit substrate, upon which the integrated antenna elements are disposed. Unfortunately, the use of low loss dielectrics which have low thermal conductivities, such as wood or glass, are generally incompatible with integrated circuits which dissipate significant power during operation.
Circuits including microprocessors can have power dissipations up to 170 W, or more. Power dissipation in electronic devices leads to heating of the circuit. Cooling measures may be required to limit junction temperatures from exceeding allowable limits of the device. Even if held within junction temperature limits, increasing chip temperatures generally degrade circuit performance and reliability of the circuit. Moreover, the speed of microprocessors is known to decrease with increasing chip temperature.
Thus, both antenna gain and heat removal are generally important factors in determining the feasibility of an integrated circuit system which includes integrated antennas. Although proximity of active devices to the heat sink reduces the junction temperature of the circuit during operation, this arrangement generally increases dielectric loss for the integrated antenna. As a result, the antenna gain is often compromised.
Thus, arrangements used to date have not been optimized for both antenna gain and heat removal. These arrangements have resulted in the inability to establish an on-chip wireless connection over a sufficient distance for certain applications, such as those requiring wireless communications over a distance of 1 cm or more.